Many urban areas have for a long time disposed of garbage by burying it in neighboring localities which are often of low grade level. Hence, such garbage disposal has also served as land fill. The buried garbage decomposes and generates gas rich in methane and carbon dioxide. Such garbage gas or land-fill gas has in some places become a nuisance because of its escape into the atmosphere. This gas, because of its methane content, generally in the range of about 50 to 70% by volume, has the potential of being a valuable energy resource rather than a distressing atmospheric pollutant. Carbon dioxide, the other principal component of land-fill gas, is generally in the range of about 25 to 45% by volume and thus is a serious deterrent to the commercial utilization of land-fill or garbage gas as a fuel gas.
The international energy crisis has given great impetus to secondary and tertiary recovery of crude oil from wells formerly considered uneconomic to exploit. Diverse processes are being proposed and utilized to stimulate the flow of crude oil from underground formations. One type of process which is finding considerable favor among oil producers involves the injection of carbon dioxide into partially depleted oil reservoirs. However, carbon dioxide has not been available to many oil fields at an economically acceptable price.
Accordingly, a principal object of this invention is to draw garbage gas from a land-fill locality in order to stop or substantially curtail the escape of the gas into the atmosphere and to utilize the withdrawn gas to stimulate the fow of crude oil from a partially depleted reservoir and, in addition, to recover from the thus utilized gas sufficiently purified methane to serve as a commercial fuel gas.
Another important object is to enhance the economic attractiveness of separating methane from land-fill gas and of stimulating oil recovery from wells with the injection of carbon dioxide by combining the two operations.
A further object is to provide a simple and flexible system for carrying out the two combined operations.
These and other objects and advantages of the invention will be evident from the description which follows.